100 FUGHT International, 21 January 1965
Control of NASA's Mariner 4 spacecraft is
exercised from this rocm—the Space Flight
Operations Facility at the Jet Propulsion
Laboratory in Pasadena, California. Radio
commands are transmitted via 85ft diameter
aerials at Goldstone, California; Johannesburg
and Woomera
3. Sixty-three Million
in Thirty-six Days:
a Progress Report
Miles
MARINER TO MARS
|ARINER 4 was launched from Cape Kennedy by Atlas
Agena D at 9.22 a.m. Eastern Standard Time on Novem-
ber 28,1964. Five minutes later, following Atlas burnout,
a magnesium-alloy shroud around the spacecraft was jettisoned.
The first major hurdle on the 325-million-mile obstacle race
towards Mars had been overcome; 23 days earlier, the launch of
Mariner 3 had failed because the spacecraft's glass-fibre shroud had
remained attached.
Six minutes after lift-off, the Agena second stage fired to inject
Mariner 4 into a parking Earth orbit. Thirty-two minutes later, at
122.8 miles over the Indian Ocean, the Agena fired a second time
to place the craft on its planned trajectory. At Agena cut-off,
Mariner was travelling at 25,598 m.p.h. relative to Earth; its signals
showed that it would pass within 151,000 miles of Mars if no
course-correction were made.
Forty-five minutes after launch, separated from the burnt-out
Agena stage, Mariner 4 began to deploy its four solar panels for
the flight. Within 16min the panels were fully deployed and the
nitrogen gas jets of its attitude control system had oriented the
panels towards the Sun (thus orienting the spacecraft on its pitch
and yaw axes but leaving it free in roll).
Now it had to "lock on" to the star Canopus, chosen as a reference
point because of its brightness and suitable position in relation to
the Earth and Sun. Mariner was equipped with a light-sensing
instrument able to detect variations in star brightness, which could
be commanded to take a second look for Canopus should it lock
on to the wrong star at the first attempt.
As programmed, the spacecraft's central computer and sequencer
ordered the search for Canopus to begin 16hr 37min after launch.
At 1.59 a.m. on November 29 the Canopus sensor was pointed in
such a direction that the spacecraft would have to roll approxi-
mately 293° to find Canopus (the craft is programmed to roll slowly
in one direction only—anticlockwise, as viewed from the Sun).
Shortly after Mariner began its controlled roll, it detected the
Earth's reflection—but sensed that the light was too bright, and
continued its manoeuvre. After 8min, at a roll angle of 100°, it
locked on to a star. This was about the dimmest possible star which
could hold Mariner's Canopus sensor. The Jet Propulsion Labora-
tory's Space Flight Operations Facility at Pasadena, nerve-centre
of Mariner flight operations, identified the star as Aldemarin.
Since the star was so dim the JPL experts believed that the spacecraft
would lose lock of its own accord and, in fact, Mariner began its
rolling search for Canopus again 5£hr later—at 8.13 a.m. EST
on November 29.
After a 107° roll lasting 16min, Mariner locked on to the star
Regulus. Again the brightness scale was low, and project officials
decided to wait one day before commanding Mariner to continue
its search for Canopus. On November 30 at 4.14 a.m. Pasadena
transmitted this command; after a 60° roll lasting 7min the craft
locked on to the star Naos in the Milky Way. At 5.45 another
search command was given; in lmin Mariner rolled 7° and fixed
on to a cluster of unnamed stars in the Milky Way.
At 5.58 it was again ordered to search and at 6 a.m. on November
30 the light sensor was attracted by the glow of a star, 100 light-
years away, nicknamed the Yellow Giant. This was Canopus, and
(at the fifth attempt) Mariner locked on, now stabilized about all
three axes. The craft was about 380,000 miles from Earth at this
time, travelling at 7,360 m.p.h. relative to the Earth.
For the next three days NASA's 85ft tracking aerials at Goldstone,
California; Woomera, Australia and Johannesburg, South Africa
were used to track the spacecraft, accurately measuring its trajectory
and determining that all parts were functioning well.
On December 3, as Mariner neared the million-mile point of its
325-million-mile journey, it was decided to attempt the midcourse
correction intended to result in a closer approach to Mars. For
this purpose, Mariner carried a small liquid-propellant motor which
could be fired for very precise periods.
The midcourse manoeuvre began at 8.05 a.m. EST on December
4, when Mariner 4 was 1,084,344 miles from Earth. Firing of the
motor would shorten the flight time by two days, and the craft
would fly past and behind the planet instead of continuing on its
present trajectory which would take it ahead of Mars.
At 5min intervals, beginning at 8.05 a.m., the Goldstone station
transmitted three quantitative commands to Mariner for it to store
in its centra] computer and sequencer. These commands, designated
QC-1, 2 and 3 called for Mariner to release its lock on the Sun and
Canopus and to orient itself to fire its rocket motor.
The QC-1 command would direct Mariner to release its Sun
lock and slowly pitch down about 44°. QC-2 called for the craft to
roll 156°, and QC-3 programmed Mariner to fire its midcourse
motor for 2O.18sec. After the spacecraft acknowledged that it had
stored these commands, two further commands were sent to prepare
for the manoeuvre. These called for immediate action and were
designated direct commands (DC). At 8.45, signal DC-29 armed
circuits to the midcourse motor. At 9.15, DC-14 removed an
inhibition which had been placed on the midcourse correction
system since launch so that it could not accidentally be triggered.
Another "inhibit" command, numbered (perhaps appropriately)
DC-13, was available for use prior to the motor burn to cancel the
manoeuvre in case of difficulty.
All was now ready to begin the midcourse manoeuvre. Another
command, DC-27, was prepared. This would transfer control of
the manoeuvre to the spacecraft itself. The DC-27 signal, sent at
9.35 a.m., switched on Mariner's gyros so that the spacecraft could
control its attitude without reference to the Sun and Canopus. It
also switched telemetry signals from scientific information from the
experiments to all engineering data so that project officials could
have the maximum information about the spacecraft during the